Patent GB-872419-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/30
Filed: 1958-03-31
Abstract: 872,419. Radio navigation. GENERAL ELECTRIC CO. Ltd., and STENNING, L. C. March 23, 1959 [March 31, 1958], No. 10331/58. Class 40(7) [Also in Groups XXXVI and XL(b) ] In a C W hyperbolic radio navigation system in which frequencies F and F(1+1/n) are transmitted respectively from spaced master and slave stations A and B, the frequency F (1+1/n) received at the mobile receiver is converted to the frequency F by means of a rotary electro-mechanical device and is compared in phase with the frequency F received from the master station, the frequency F(1+1/n) generated at the slave station being derived from the frequency F received from the master station by means of a similar rotary electro-mechanical device. The frequency F may be 15 kc./s. and n may be such that F/n = 30 c/s. As shown in Fig. 3, an oscillator 43 at the slave station is automatically phase locked to the frequency F from the master station and two outputs of frequency F from the oscillator 43 are applied in phase quadrature to orthogonal stator coils 61, 62 of a resolver 240 whose rotor coil 63 is rotated continuously at a speed of F/n c/s by a synchronous motor 49 controlled via a frequency divider 48 (division factor n) by another output from the oscillator 43, the output of frequency F(1+1) from the n rotor coil 63 being transmitted from the slave station. At the mobile receiver, Fig. 4, oscillators 98 and 99 are automatically phase locked to the received master and slave frequencies F and F (1+1/n) respectively and the output F(1+1/n) from the oscillator 99 is applied in phase quadrature to two orthogonal stator coils 116, 117 of a resolver 28 whose rotor coil 118 is driven by a synchronous motor 119 controlled via a frequency divider 121 (division factor n) from the output of the rotor 118 such that the frequency of said output is equal to n/n+1 times the frequency of the signals applied to the stator coils 116, 117 so that:- output frequency = n/n+1 F(1+1/n)=F Alternatively the division factor of the frequency divider 121 may be r and the motor 119 is coupled to the rotor 118 through a gear of ratio s such that r s = n. The output F from the rotor 118 is also applied together with an output F from the oscillator 98 to a phase comparator 30, Fig. 8 (not shown, see Group XXXVI), which indicates the relative phase of the two inputs. The zero of the phasemeter may be adjusted by a phase shifter in series with one of the inputs or by a slipping clutch, Fig. 7 (not shown), between the motor 119 and the rotor 118. In a modification the inductive resolvers 240, Fig. 3, and 28, Fig. 4, are replaced by electrostatic devices, Fig. 11 (not shown). The invention is described in detail as applied to a system defining two intersecting sets of isophase lines and comprising a master station A and two spaced slave stations B and C transmitting respectively frequencies F, F(1+1/n) and F(1-1/n). At the receiver, Fig. 4, the three signals are separated by crystal filters, 22, 23, 24, Figs. 5 and 6 (not shown, see Group XL(b) ) and a signal of frequency F is derived from the C slave signal F(1-1/n by an additional channel similar to the one for the B slave signal described above, the only difference being that the rotors 118 and 122 of the frequency converters 28, 29 rotate in opposite directions. Separate A.G.C. circuits 92, 93, 94 are provided for the separated signals and a further A.G.C. circuit 82 is provided for the receiver amplifier 81. If a third slave is required it may operate at a frequency of F(2/n), the corresponding frequency dividers having division factors of n/2. Additional fine and coarse indications may be provided by multiplying and dividing the frequencies of the received signals by a factor m and applying the resultant signals to additional channels similar to those described above. If the oscillators 98, 99 and 100 in the receiver, Fig. 4, are sufficiently stable, the transmitted signals may be interrupted for short periods for the transmission of intelligence by means of Morse signals. The invention is also applicable to a system, Fig. 10 (not shown) comprising two or three spaced master stations transmitting frequencies Fl, F2, F3 respectively, each master station being associated with a single slave station transmitting a corresponding frequency F1(11/n), F2(11/n) or F3(11/n). According to the Provisional Specification the frequency F(1+1/n) at the slave station B, Fig. 3, may be produced by modulating the output F from the oscillator 43 with the output F/n from the frequency divider 48 and in the mobile receiver, Fig. 4, the synchronous motor 119 may be controlled by an oscillator phase locked to the output from the frequency divider 121. Specification 637,996 is referred to.